I said just down that comment string that they get tired before I do.
One of them never touched herself before so usually when she got close to cumming (her legs spasmed a bit, so that was my cue) she would push me away and say she was too sensitive. Tried telling her to masturbate and get used to the sensation for a couple years but she never did, wasn't even religious, just really really ashamed of doing it.
The other was just really dry and took some time with oral just for me to be able to put it in her. I started using condoms so she could stop taking the pill and her fluids eventually came back naturally, so where before she would either get sore or ask me to stop so she could breathe a bit, now only the latter would happen.
I started dating my current gf after I did a lot of cardio exercise + rugby. I'm not a lean motherfucker, but I can take from 30 minutes to an hour so she just gets tired before I do sometimes. Thank god she wasn't a virgin, so she knew how to do good oral after so I didn't have to sleep with blue balls until the next day.